This invention relates to a device for horizontal continuous casting of metals or alloys, in particular steels, having as essential components a cooled ingot mold and a strand withdrawal device displaceable in the direction of the longitudinal axis of the strand, with aftercoolers optionally connected downstream of the mold and before the withdrawal device.
In horizontal continuous casting of metals, the strand formed in the casting mold, which has not yet completely solidified, is drawn out of the mold by means of the strand withdrawal device. In particular with alloys melting at elevated temperatures, such as, for instance, steels, the strand withdrawal occurs preferably in steps. By pausing between the individual withdrawal steps or by pushing back of the strand, the contraction occurring during cooling is compensated for, heat cracks are avoided, and solid welding of the individual strand skin sections respectively formed in the mold is achieved.
Basically, two different arrangements of strand withdrawal devices are known. One such arrangement, that is today in lesser use, has clamps that seize the strand and move it in the desired manner. This type of drive is not entirely accurate since the relatively large mass of the jaws must be moved so that gears of corresponding size having relatively large clearances must be used. Moreover, the danger of damaging the strand surface is presented by such an arrangement.
Preferably, accurate strand withdrawal is accomplished today by means of driving rollers or pairs of driving rollers which engage the strand directly. Driving rollers guarantee a steady contact between the strand and the withdrawal device, thereby bringing about an accurate withdrawal of the strand.
Representative of the large number of prior art references describing horizontal continuous casting devices, as well as those that relate to strand withdrawal devices; are German Pat. Nos. 1,583,611 and 2,340,636.
In the continuous casting cycle, the metal, after leaving the molten metal container, is subjected to profiling in the ingot mold and to an optional cooling cycle in aftercoolers, during which there occurs a progressive cooling of the strand and an increase in the thickness of the strand skin. After the cast strand has left the ingot mold and the optional aftercoolers, and before it is seized by the strand withdrawal arrangement, e.g., the driving rollers, further cooling takes place. Depending on the shrinkage or expansion behavior of the metal or alloy, dimensional changes also occur along this path, which changes become noticeable, particularly in the longitudinal direction of the strand. In addition to these longitudinal changes, during the cooling and continuous solidification of the strand, which may differ from metal to metal and from alloy to alloy, phase changes may occur within the already solidified strand skin which may result in dimensional constancy rather than the customary shrinkage of the strand during cooling.
In the German Pat. No. 1,583,611 referred to above, there is described a strand withdrawal device in which the driving roller carrying frame is reciprocated in the longitudinal direction of the strand during the strand withdrawal cycle. A strand withdrawal frame, similarly movable in oscillatory fashion in the longitudinal direction of the strand, but that is outfitted with clamping jaws, is disclosed in Austrian Pat. No. 277,489. In these two devices, the points of reversal of the oscillating movement of the frame, or of the strand withdrawal elements, is preset to be constant. Thus, in every cycle of reciprocating movement the initial seizing of the strand by the strand withdrawal elements occurs at the same point along the path of the strand.
As a result, even though the withdrawal device is designed to be movable and moves during withdrawal, the strand withdrawal operation cannot be addressed individually to the specific metal or alloy to be cast and to its specific behavior during the cooling cycle, to insure that the withdrawal elements always engage the strand precisely at the point at which the strand has cooled sufficiently and is strong enough to avoid a break or damage. Since this point differs from metal to metal and, in the same metal, varies according to the cross-sectional dimension of the withdrawn strand, it is necessary, for safety considerations, in order to avoid damaging of the strand and to prevent breaks or the like that affect operations, to maintain the spacing between engagement of the strand by the first strand withdrawal element and the end of the ingot or the aftercooler greater than would be necessary on the basis of the respective "metallurgical length", the depth of the sump, or the like. ln plants having an oscillating frame in accordance with the arrangements known in the art, such individual setting of the point at which the strand withdrawal occurs has not been provided for.